physics investigatory project

2. Contents
 Certificate
 Acknowledgement
 Introduction
 Principle of A.C. Generator
 Construction of A.C. Generator
 Theory
 Circuit Diagram
 Working of A.C. Generator
 Expression for Instaneous e.m.f. produced
 Result
 Applications of A.C. Generator
 Bibliography

3. Certificate
This is to certify that Aditya Singh, a student of class
XII-A has successfully completed the project under the
guidance of Mr. Nitin Khabrani (Physics Teacher)
During the academic year 2016-17 in partial fulfillment of
chemistry practical examination conducted by CBSE,
New Delhi.
Signature of external examiner Signature of chemistry teacher

4. It would my utmost pleasure to express my
sincere thanks to my physics teacher
MR. NITIN KHABRANI in providing
a helping hand in this project.
His valuable guidance and support and
supervision all through this project are
responsible for attaining its present form.
Acknowledgement

5. Introduction
A.C. Generator means Alternating current generator. It is a
device which is used to convert mechanical energy into
electrical energy.
A.C. generator forces electric current to flow through an
external circuit. The source of mechanical energy may be a
reciprocating or turbine steam engine, water falling through
a turbine or waterwheel, an internal combustion engine,
a wind turbine, a hand crank, compressed air ,or any other
source of mechanical energy.

6. Principle of A.C. Generator
It is based on the principle of electro magnetic
induction, i.e., whenever amount of magnetic flux
linked with a coil changes, an e.m.f. is induced in the
coil. The direction of current induced is given by
Fleming’s right hand rule.

7. Construction of A.C. generator
The A.C. Generator is consist of four main parts :
(1) THE COIL (ARMATURE) :
A rectangular coil ABCD consist of a large number
of turns of copper bound over a soft iron core is called
armature. The soft iron core is used to increase the magnetic
flux.
(2) MAGNETIC FIELD :
It is usually a permanent sponge magnet having concave
poles. The armature is rotated of a magnet so that axis of the
armature is perpendicular to magnetic field lines.

8. (3) SLIP RINGS :
Slip rings are the magnetic rings which are connected
in the terminal of the armature. These rings are rotated
with the coil and these are use to draw the current from
the generator.
(4) BRUSHES :
The brushes B1 & B2 are just touch the slip rings. They are
not rotating with the coil and these brushes leads to the
output of load resistance.

9. Theory
1. The strong magnetic field is produced by a current flow through the
field coil of the rotor.
2. The field coil in the rotor receives excitation through the
use of slip rings and brushes.
3. Two brushes are spring-held in contact with the slip rings to provide the
continuous connection between the field coil and external circuit.
4. The armature is contained within the windings of the stator and is
connected to the output.
5. Each time the rotor makes one complete revolution, one complete
cycle of AC is developed.
6. A generator has many turns of wire wound into the slots of the rotor.
7. The magnitude of AC voltage generated by an AC generator is
dependent on the field strength and speed of the rotor.
8. Most generators are operated at a constant speed; therefore, the
generated voltage depends on field excitation, or strength.

10. Circuit Diagram

11. Working of an A.C. Generator
The coil is rotated in anti-clock wise direction. In the first
half rotation the arm AB is moving outward and CD is
moving inward. So the e.m.f. is induced in the arm AB
from A to B. And in the arm CD from C to D. After half
rotation (in the second half). The arm CD is moving
outward and AB is moving inward. In this time current is
induced in arm CD from D to C. And in arm AB from B to
A. In the second half rotation the current direction is
changing so in this generator AC is produced.

12. Expression for Instaneous
e.m.f. produced
Let position of the coil at any time t. It's make angle θ with
vertical. If w is uniform angular speed
of the coil.
Then θ =ωt
B be the strength of magnetic field n be the number of
turns in the coil and A area of the coil then magnetic flux
with the coil in this position is given by :
Φ = nBA Cosθ = nBA Cos ωt.

13. differentiate w.r.t. time :-
𝑑∅
𝑑𝑡
=nBA
𝑑 cos(𝜔𝑡)
𝑑𝑥
𝑑∅
𝑑𝑡
= nBA-sin(𝜔𝑡)𝜔
𝑑∅
𝑑𝑡
= -nBA 𝜔 sin(𝜔𝑡)𝜔
ε=-
𝑑∅
𝑑𝑡
=-(-nBA 𝜔 sin(𝜔𝑡)𝜔)
Maximum value of e.m.f. say so 𝜺°
ε = ε° sin(𝜔𝑡)

14. Result :-
Hence, maximum value of instantaneous
e.m.f. in a AC Generator is given by
𝜺 = 𝜺° sin(𝝎𝒕)

15. Applications of A.C. Generator
1. Aircraft auxiliary power generation, wind generators,
high speed gas turbine generators.
2. Hybrid electric vehicle (HEV) drive systems, automotive
starter generators.
3. An ac generator, or 'alternator', is used to produce ac
voltages for transmission via the grid system or, locally,
as portable generators.
4. All of our household appliances runs on ac current.
Ex: Refrigerator, washing machines, oven, lights, fan etc.
5. The main advantage of AC is ease of power distribution.
It is more efficient to use high voltage to distribute power,
but it is not safe to have high voltage at home. It is easy to
step up (and step down) AC voltage using a transformer.

16. Bibliography
• CBSE Lab manual
• Help of Physics Teacher
• NCERT Textbook
• Websites:-
www.google.com
www.wikipedia.com